Silicate phosphors

ABSTRACT

The present invention relates to Eu-, Sm- or Pr-doped silicate compounds, to a process for the preparation thereof and to the use thereof as conversion phosphors. The present invention also relates to an emission-converting material comprising at least the conversion phosphor according to the invention and to the use thereof in light sources, in particular pc-LEDs (phosphor converted light emitting devices). The present invention furthermore relates to light sources, in particular pc-LEDs, and lighting units which contain a primary light source and the emission-converting material according to the invention.

The present invention relates to Eu-, Sm- or Pr-doped silicatecompounds, to a process for the preparation thereof and to the usethereof as conversion phosphors. The present invention also relates toan emission-converting material comprising at least the conversionphosphor according to the invention and to the use thereof in lightsources, in particular pc-LEDs (phosphor converted light emittingdevices). The present invention furthermore relates to light sources, inparticular pc-LEDs, and lighting units which contain a primary lightsource and the emission-converting material according to the invention.

For more than 100 years, inorganic phosphors have been developed inorder to adapt the spectra of emissive light screens, X-ray amplifiersand radiation or light sources in such a way that they meet therequirements of the respective area of application in as optimal amanner as possible and at the same time consume as little energy aspossible. The type of excitation, i.e. the nature of the primaryradiation source and the requisite emission spectrum, is of crucialimportance here for the choice of host lattice and the activators.

In particular for fluorescent light sources for general lighting, i.e.for low-pressure discharge lamps and light-emitting diodes, novelphosphors are constantly being developed in order further to increasethe energy efficiency, colour reproduction and stability.

There are in principle three different approaches to obtainingwhite-emitting inorganic LEDs (light-emitting diodes) by additive colourmixing:

-   -   (1) The RGB LEDs (red+green+blue LEDs), in the case of which        white light is generated by mixing the light from three        different light-emitting diodes which emit in the red, green and        blue spectral region.    -   (2) The UV LED+RGB phosphor systems, in the case of which a        semiconductor emitting in the UV region (primary light source)        emits the light to an environment in which three different        phosphors (conversion phosphors) which emit in the red, green        and blue spectral region are excited.    -   (3) Complementary systems, in the case of which an emitting        semi-conductor (primary light source) emits, for example, blue        light, which excites one or more phosphors (conversion        phosphor), which emit light, for example, in the yellow region.        By mixing the blue and yellow light, white light is then        generated. Alternatively, it is possible to use a phosphor        mixture which emits green and red light.

Binary complementary systems have the advantage that they are capable ofproducing white light with only one primary light source and—in thesimplest case—with only one conversion phosphor. The best-known of thesesystems consists of an indium aluminium nitride chip as primary lightsource, which emits light in the blue spectral region, and acerium-doped yttrium aluminium garnet (YAG:Ce) as conversion phosphor,which is excited in the blue region and emits light in the yellowspectral region. However, improvements in the colour rendering index andthe stability of the colour temperature are desirable.

In the case of the use of a blue-emitting semiconductor as primary lightsource, the binary complementary systems thus require a yellowconversion phosphor or green- and red-emitting conversion phosphors inorder to reproduce white light. If, as an alternative, the primary lightsource used is a semiconductor which emits in the violet spectral regionor in the near-UV spectrum, either an RGB phosphor mixture or adichromatic mixture of two complementary light-emitting conversionphosphors must be used in order to obtain white light. In the case ofthe use of a system having a primary light source in the violet or UVregion and two complementary conversion phosphors, light-emitting diodeshaving a particularly high lumen equivalent can be provided. A furtheradvantage of a dichromatic phosphor mixture is the lower spectralinteraction and the associated higher package gain.

In particular, inorganic fluorescent powders which can be excited in theblue and/or UV region of the spectrum are therefore gaining ever-greaterimportance today as conversion phosphors for light sources, inparticular for pc-LEDs.

In the meantime, many conversion phosphors have been disclosed, forexample alkaline-earth metal orthosilicates, thiogallates, garnets andnitrides, each of which are doped with Ce³⁺ or Eu²⁺.

However, there is a constant demand for novel conversion phosphors whichcan be excited in the blue or UV region and emit light in the visibleregion of the excitation spectrum.

The object of the present invention was therefore to provide novelmaterials with which radiation in the blue or UV region can be convertedefficiently into radiation in the visible spectrum.

It is known that, on photon irradiation at 160 or 254 nm, hexagonalsolid-state compounds of the formula BaZr_(1-x)Hf_(x)Si₃O₉ (x equal to 0to 1) of the bazirite mineral type exhibit intense UV and blueluminescence having an emission maximum at 260 nm or 440 nmrespectively. It has now surprisingly been observed by the inventors ofthe present application that, when some of the Zr or Hf ions in themineral have been replaced by Eu, Pr or Sm ions, a cyan-emitting orred-emitting phosphor can be obtained which emits with a quantum yieldof up to 90%.

The present invention therefore relates firstly to a compound of theformula I

(Ba_(y)Sr_(1-y))Zr_(1-x)Hf_(x)Si₃O₉   (I),

where x is in the range from 0 to 1 and, independently thereof, y is inthe range from 0 to 1,

characterised in that some of the Zr or Hf ions of the compound of theformula I have been replaced by Eu, Pr or Sm ions. An alkali-metal ionis additionally present in the compound if Eu or Pr or Sm in theoxidation state +III has been incorporated.

An ion exchange of this type is also referred to as “doping”. To thisextent, the Eu, Pr or Sm ions in this application are also referred toas doping ions.

It is preferred in a variant of the invention for x to be equal to 0 or1, i.e. the compound is either (Ba_(y)Sr_(1-y))ZrSi₃O₉ or(Ba_(y)Sr_(1-y)) HfSi₃O₉. This variant of the invention has theadvantage of simplified preparation of the materials, since the numberof different starting materials can be kept small.

It is furthermore preferred for 0.1 or 20 mol % of the Zr or Hf ionsrespectively in the compound of the formula I according to the inventionto have been replaced by Eu, Pr or Sm ions, more preferably 0.2 to 10mol % and most preferably 0.3 to 5 mol %.

In an embodiment of the present invention, the Eu ions are present indivalent form, meaning that a tetravalent Zr or Hf ion has been replacedby two Eu ions. In this case, a cyan-emitting phosphor having a veryhigh quantum yield of up to 90% is provided. FIGS. 3 and 5 show emissionspectra for the compounds BaZrSi₃O₉:Eu²⁺ and BaHfSi₃O₉:Eu²⁺ according tothe invention with different doping contents. The absorption is slightlyred-shifted with increasing doping. In this way, the absorption maximumcan be adjusted correspondingly depending on the doping content. Thesecompounds which are preferred in accordance with the invention areparticularly suitable for excitation in the near-UV region or in theblue region.

In a further embodiment, the tetravalent Zr or Hf ions of the compoundof the formula I may have been replaced by trivalent metal ions selectedfrom the group consisting of Pr³⁺, Sm³⁺, Eu³⁺ and combinations thereof.Since the replaced Zr or Hf ions are tetravalent ions, univalentalkali-metal ions are also present in equimolar number to the trivalentdoping ions for charge compensation. With respect to the alkali-metalions, reference is made here to so-called co-doping. Possiblealkali-metal ions to be employed are Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺, in whichNa⁺ is preferred. Figures 6 to 8 show reflection spectra, excitationspectra and emission spectra for the compounds BaZrSi₃O₉:Sm³⁺/Na⁺,BaHfSi₃O₉:Sm³/Na⁺, BaZrSi₃O₉:Eu³⁺/Na⁺, BaHfSi₃O₉:Eu³⁺/Na⁺,BaZrSi₃O₉:Pr³⁺/Na⁺ and BaHfSi₃O₉:Pr³⁺/Na⁺ according to the invention.These compounds, which are likewise preferred in accordance with theinvention, are particularly suitable for excitation in the UV region at150-270 nm.

In addition, the emission colour of the compound of the formula I canalso be influenced via the barium or strontium content. Thus, a highbarium content (0.7<y≦1) or even a compound which contains no strontiumat all (y=1) may be preferred if the emission is to be in the cyan orgreen wavelength region. Conversely, a compound having a high strontiumcontent (0≦y<0.3) or even a barium-free compound (y=0) may be preferredif emission in the orange-red region is desired.

The present invention furthermore relates to a process for thepreparation of a compound of the formula I, comprising the followingprocess steps:

-   -   a) provision of a barium and/or strontium source, a zirconium        and/or hafnium source, a silicon source and a source of one of        the metals samarium, praseodymium or europium;    -   b) mixing of the sources provided in step a); and    -   c) sintering of the sources mixed in step b) at a temperature in        the range from 1000 to 1700° C.

A barium or strontium source is taken to mean in accordance with theinvention an inorganic or organic barium or strontium compound which iscapable of conversion into barium oxide or strontium oxide oncalcination. Possible barium or strontium sources are barium carbonateor strontium carbonate, barium sulfate or strontium sulfate, bariumnitrate or strontium nitrate, barium oxalate or strontium oxalate,barium oxide or strontium oxide and barium halide or strontium halide,barium peroxide or strontium peroxide, in which barium carbonate orstrontium carbonate is particularly preferred. It may be preferred herefor barium and strontium already to be present in the “source” in theratio to one another in which these alkaline-earth metal ions are alsoto be present in the compound of the formula I according to theinvention.

A zirconium or hafnium source is taken to mean in accordance with theinvention an organic or inorganic zirconium or hafnium compound whichcan be decomposed on calcination to give an oxide. In particular,oxides, oxysulfates, or oxalates of zirconium or hafnium, morepreferably the oxides ZrO₂ or HfO₂, are employed here. It may also bepreferred here for zirconium and hafnium already to be present in the“source” in the ratio to one another in which these metal ions are alsoto be present in the compound of the formula I according to theinvention.

A silicon source is taken to mean in accordance with the invention aninorganic or organic silicon source, where an inorganic silicon sourceis again preferred here. Silicon dioxide is particularly preferablyemployed as silicon source here.

The source of one of the metals samarium, praseodymium or europiumemployed can be any inorganic or organic compounds of these metals whichcontain these metals in divalent or trivalent form and can be convertedinto an oxide on calcination. Use can be made here, for example, of theoxides, oxalates, acetates, nitrates, sulfates or carbonates. Particularpreference is given to sources of these metals in which the metals arepresent in trivalent form. Especial preference is given here to the useof the oxides of samarium, praseodymium or europium, even morepreferably Sm₂O₃, Pr₂O₃ and Eu₂O₃.

The sources of barium or strontium, zirconium or hafnium, silicon andthe metals samarium, praseodymium or europium provided are mixedvigorously with one another in step b). The mixing is preferably carriedout in a mortar, in which a grinding agent, such as, for example,acetone, is preferably additionally added. It is furthermore preferredfor a borate salt (for example an alkali-metal borate, such as Na₂B₄O₇)or boric acid to be added as sintering aid during the step of mixing theabove-mentioned sources.

After the mixing of the components in step b), the powder is preferablydried in a temperature range from 100 to 300° C. and subsequentlysubjected to a temperature treatment in the range from 1000 to 1700° C.,more preferably 1200 to 1600° C.

If doping with a divalent doping ion, preferably Eu²⁺, in the compoundof the formula I is desired, the temperature treatment is preferablycarried out for 2 to 4 h. If a source of the metals europium, samariumor praseodymium in which the metals are present in their trivalent formis employed for this purpose in step a) of the process according to theinvention, the temperature treatment is preferably carried out in areducing atmosphere. The reductive conditions here are established, forexample, using carbon monoxide, forming gas, hydrogen or at least vacuumor an oxygen-deficiency atmosphere, preferably in a stream of nitrogen,preferably in a stream of N₂/H₂ and particularly preferably in a streamof N₂/H₂/NH₃. It is particularly preferred to prepare firstly anatmosphere comprising carbon monoxide and subsequently an atmospherecomprising forming gas during the temperature treatment. If a source ofthe metals europium, samarium or praseodymium in which the metals arepresent in their divalent form is employed, it is not necessary for thetemperature treatment to be carried out in a reducing atmosphere;however, it is preferred to work under a protective-gas atmosphere (forexample Ar, He, Ne or N₂).

If doping with a trivalent doping ion in the compound of the formula Iis desired, it is not necessary for the temperature treatment to becarried out in a reducing atmosphere. Here, the temperature treatmentcan preferably be carried out in air for preferably 2 to 4 h.

As already mentioned above, the compounds of the formula I according tothe invention doped with a trivalent doping ion contain an alkali-metalion for charge compensation. It is therefore preferred for an inorganicalkali-metal compound, preferably an alkali-metal salt, such asalkali-metal carbonate, alkali-metal sulfate or alkali-metal chloride,more preferably alkali-metal carbonate and most preferably sodiumcarbonate, additionally to be employed in step a) of mixing in theprocess according to the invention for the preparation of compounds ofthe formula I which contain a trivalent doping ion.

The sources employed in step a) of the process according to theinvention are weighed out in a ratio to one another with respect to themolar content of the metals such that the molar ratio corresponds to thedesired ratio in the end product (compound of the formula I).

The sintering aid is preferably added in an amount in the range from 0to 8 mol %, based on the total amount of all sources employed in step a)of the process according to the invention.

The compound of the formula I is obtained in the form of particles bythe process according to the invention through the sinter cake beingground with grinding beads, sieved and subsequently classified. Thecompound of the formula I according to the invention is preferably inthe form of particles. The particles preferably have a particle size inthe range from 50 nm to 30 μm and more preferably from 1 μm to 20 μm.The particles of the compound of the formula I can also have a surfacewhich carries functional groups which facilitate chemical bonding tosurrounding binders comprising, for example, epoxy or silicone resinand/or glasses or plastics, such as acrylates, polycarbonates. Thesefunctional groups can be esters bonded, for example, via oxo groups, orother derivatives which are able to form links with constituents of thebinders. Such surfaces have the advantage that homogeneous mixing of thephosphors into the binder is facilitated. Furthermore, the rheologicalproperties of the phosphor/binder system and also the pot lives canthereby be adjusted to a certain extent. Processing of the mixtures canthus be simplified.

The present invention furthermore relates to the use of the compound ofthe formula I as phosphor, in particular as conversion phosphor.

In the present application, the term “conversion phosphor” is taken tomean a material which absorbs radiation in a certain wavelength regionof the electromagnetic spectrum, preferably in the blue or UV region, inparticular in the near-UV region, and emits visible light in anotherwavelength region of the electromagnetic spectrum.

The present invention furthermore relates to an emission-convertingmaterial comprising a compound of the formula I according to theinvention. The emission-converting material may consist of the compoundof the formula I and in this case would be regarded as equivalent to theterm “conversion phosphor” defined above.

However, it is preferred for the emission-converting material accordingto the invention to comprise further conversion phosphors in addition tothe conversion phosphor according to the invention. In this case, theemission-converting material according to the invention comprises amixture of at least two conversion phosphors, where one of them is acompound of the formula I. It is particularly preferred for the at leasttwo conversion phosphors to be phosphors which emit light of wavelengthswhich are complementary to one another. If the conversion phosphoraccording to the invention is, for example, a cyan-emitting phosphor(divalent Eu), this is preferably employed in combination with anorange-emitting conversion phosphor. Alternatively, the cyan-emittingconversion phosphor according to the invention can also be employed incombination with (a) green- and red-emitting conversion phosphor(s). Ifthe conversion phosphor according to the invention is a red-emittingphosphor (trivalent dopant), this is preferably employed with (a) cyan-and green-emitting phosphor(s). It is thus particularly preferred forthe conversion phosphor according to the invention to be employed incombination with one or more further conversion phosphors in theemission-converting material according to the invention, which thentogether preferably emit white light.

Thus, for example, a cyan-emitting conversion phosphor according to theinvention can be employed in combination with (Sr,Ca)₂SiO₄:Eu as furtherconversion phosphor. FIG. 1 shows a colour diagram with the colourvalues of BaZrSi₃O₉:Eu²⁺ and BaHfSi₃O₉:Eu²⁺ and of (Sr,Ca)₂SiO₄:Eu asorange emitter.

The further conversion phosphors are preferably selected from the groupconsisting of sulfides, silicates, aluminates, borates, nitrides,oxynitrides, siliconitrides and alumosiliconitrides which are doped withEu²⁺, Ce³⁺ or Mn²⁺. The following Table 1 lists diverse examples of suchphosphors.

TABLE 1 Red-, orange-, yellow-, green- and cyan-emitting phosphors whichcan be used in combination with the phosphors claimed here. CompositionEmission colour λ_(max) [nm] LaAl(Si_(6−z)Al_(z))—(N_(10−z)O_(z)):CeCyan 460-500 CaSi₂O_(2−z)N_(2+2/3z):Eu Green 534-562 γ-AlON:Mn—Mg Green512 (Ba₁−_(x)Sr_(x))₂SiO₄:Eu Green 520-560 SrGa₂S₄:Eu Green 535SrSi₂N₂O₂:Eu Green 535-554 SrAlSi₄N₇:Eu Cyan and red 500, 632Ba₂ZnS₃:Ce, Eu Cyan and red 498, 655 LaSr₂AlO₅:Ce Yellow 556Tb₃Al₅O₁₂:Ce Yellow 545-555 Sr₂Si₅N₈:Ce Yellow 553 CaSi₂N₂O₂:Eu Yellow565 (Sr_(1−x)Ca_(x))₂SiO₄:Eu Orange 560-600 MgS:Eu Orange 580 Sr₃SiO₅:EuOrange 570 Ca₂BO₃Cl:Eu Orange 573 Li-α-SiAlON:Eu Orange 573 CaAlSiN₃:CeOrange 580 SrLi₂SiO₄:Eu Orange 562 Ca₂SiS₄:Eu Orange to red 550, 660Y₃Mg₂AlSi₂O₁₂:Ce Orange to red 600 (Ca_(1−x−y)Sr_(x)Ba_(y))₂Si₅N₈:EuOrange to red 580-640 (Ca_(1−x)Sr_(x))AlSiN₃:Eu Red 630-650Lu₂CaMg₂Si₃O₁₂:Ce Red 605 Sr₃(Al₂O₅)Cl₂:Eu Red 610 Sr₂Si₅N₈:Eu Red 625CaSiN₂:Ce Red 625 SrSiN₂:Eu Red 670-685 (Ca_(1−x)Sr_(x))S:Eu Red 610-655SrSiO₅:Ce, Li Cyan to red 465-700 Ca-α-SiAlON:Eu Cyan to red 500-700MgSiN₂:Mn Yellow to red 550-800

In the context of this application, the term cyan light is applied tolight whose intensity maximum is at a wavelength between 460 and 505 nm,the term green light is applied to light whose intensity maximum is at awavelength between 505 and 545 nm, the term yellow light is applied tolight whose intensity maximum is at a wavelength between 545 and 565 nm,the term orange light is applied to light whose intensity maximum is ata wavelength between 565 and 600 nm, and the term red light is appliedto light whose maximum is at a wavelength between 600 and 670 nm.

If a conversion phosphor according to the invention is mixed with atleast one further conversion phosphor, the ratio of conversion phosphoraccording to the invention to the further phosphor is preferably 20:1 to1:20, particularly preferably 10:1 to 1:10 and especially preferably 5:1to 1:5, based on the total weight of the phosphors.

The present invention furthermore relates to the use of theemission-converting material according to the invention in a lightsource.

The present invention furthermore relates to a light source whichcontains a primary light source and the emission-converting materialaccording to the invention.

Here too, it may be especially preferred for the emission-convertingmaterial to comprise at least one further conversion phosphor inaddition to the conversion phosphor according to the invention, so thatthe light source preferably emits white light or light having a certaincolour point (colour-on-demand principle).

In a preferred embodiment, the light source according to the inventionis a pc-LED. A pc-LED generally contains a primary light source and anemission-converting material. The emission-converting material accordingto the invention can for this purpose either be dispersed in a resin(for example epoxy or silicone resin) or, given suitable size ratios,arranged directly on the primary light source or remote therefrom,depending on the application (the latter arrangement also includes“remote phosphor technology”). The advantages of remote phosphortechnology are known to the person skilled in the art and are revealed,for example, in the following publication: Japanese Journ. of Appl.Phys., Vol. 44, No. 21 (2005), L649-L651.

The primary light source can be a semiconductor chip, a luminescentarrangement based on ZnO, TCO (transparent conducting oxide), ZnSe orSiC, an arrangement based on an organic light-emitting layer (OLED) or aplasma or gas-discharge source, most preferably a semiconductor chip.Possible forms of light sources of this type are known to the personskilled in the art.

If the primary light source is a semiconductor chip, it is preferably aluminescent indium aluminium gallium nitride (InAlGaN), in particular ofthe formula In_(i)Ga_(j)Al_(k)N, where 0≦i, 0≦j, 0≦k, and i+j+k=1.

As already mentioned, the emission-converting material according to theinvention can, in particular for use in light sources, in particularpc-LEDs, also be converted into any desired outer shapes, such asspherical particles, flakes and structured materials and ceramics. Theseshapes are summarised under the term “mouldings”. The mouldings areconsequently emission-converting mouldings.

The production of a, for example, ceramic emission-converting mouldingcomprising the emission-converting material is preferably carried outanalogously to the process described in DE 10349038. In this case, thecompound of the formula I according to the invention is preferablysubjected to isostatic pressing, optionally with a further materialwhich serves as matrix, and applied directly, in the form of ahomogeneous thin and non-porous flake, to the surface of a primary lightsource in the form of a chip. This has the advantage that nolocation-dependent variation of the excitation and emission of theconversion phosphor takes place, with the result that the LED fittedtherewith emits a homogeneous light cone of constant colour and has highlight output. The ceramic emission-converting moulding may, ifnecessary, be fixed to the chip substrate using a water-glass solution.

In a preferred embodiment, the ceramic emission-converting moulding hasa structured (for example pyramidal) surface on the side opposite asemi-conductor chip. As much light as possible can thus be coupled outof the ceramic emission-converting moulding. The structured surface onthe ceramic emission-converting moulding is preferably produced by thecompression mould in the case of isostatic pressing having a structuredpress platen and thus embossing a structure into the surface. Structuredsurfaces are desired if the thinnest possible ceramicemission-converting mouldings or flakes are to be produced. The pressingconditions are known to the person skilled in the art (see J.Kriegsmann, Technische keramische Werkstoffe [Industrial CeramicMaterials], Chap. 4, Deutscher Wirtschaftsdienst, 1998). It is importantthat the pressing temperatures used are ⅔ to ⅚ of the melting point ofthe substance to be pressed.

Also possible, however, are embodiments for the application of theemission-converting material according to the invention to a chip asprimary light source in which the emission-converting material isapplied in silicone as a layer. The silicone here has a surface tension,meaning that the layer of the emission-converting material is notuniform at a microscopic level or the thickness of the layer is notentirely constant. However, this means that the efficacy of the layercomprising the conversion phosphors is not or at least not significantlyrestricted.

The invention furthermore relates to a lighting unit, in particular forthe backlighting of display devices, which contains at least one lightsource according to the invention. Lighting units of this type areemployed principally in display devices, in particular liquid-crystaldisplay devices (LC displays), having backlighting. The presentinvention therefore also relates to a display device of this type.

In a variant of the invention, the optical coupling between theemission-converting material and the primary light source (in particularsemiconductor chip) is preferably effected by a light-conductingarrangement. This makes it possible for the primary light source to beinstalled at a central location and to be optically coupled to theemission-converting material by means of light-conducting devices, suchas, for example, optical fibres. In this way, it is possible to achievelamps adapted to the lighting wishes which merely consist of one or moredifferent conversion phosphors, which may be arranged to form a lightscreen, and an optical waveguide, which is coupled to the primary lightsource. In this way, it is possible to place a strong primary lightsource at a location which is favourable for electrical installation andto install lamps comprising emission-converting materials, which arecoupled to the optical waveguides, at any desired locations withoutfurther electrical cabling, merely by laying optical waveguides.

The following examples and figures are intended to illustrate thepresent invention. However, they should in no way be regarded aslimiting. All compounds or components which can be used in thepreparations are either known and commercially available, or can besynthesised by known methods. It furthermore goes without saying that,both in the description and in the examples, the added amounts of thecomponents in the compositions always add up to a total of 100%. Percent data given should always be regarded in the given context. However,they usually always relate to the weight of the part-amount or totalamount indicated.

Even without further comments, it is assumed that a person skilled inthe art will be able to utilise the above description in the broadestscope. The preferred embodiments should therefore merely be regarded asdescriptive disclosure which is absolutely not limiting in any way. Thecomplete disclosure content of all applications and publicationsmentioned above and below is incorporated into this application by wayof reference.

DESCRIPTION OF THE FIGURES

FIG. 1: CIE 1931 colour diagram with the colour values of BaZrSi₃O₉:Eu²⁺and BaHfSi₃O₉:Eu²⁺ and of (Sr,Ca)₂SiO₄:Eu as orange emitter.

FIG. 2: X-ray powder diffraction patterns of BaZrSi₃O₉:Eu²⁺ with 2 mol %and 0.5 mol % europium doping compared with undoped BaZrSi₃O₉ (measuredusing Cu Kai radiation).

FIG. 3: Emission spectra of BaZrSi₃O₉:Eu²⁺ (λ_(ex)=380 nm) with 2 mol %and 0.5 mol % europium doping.

FIG. 4: X-ray powder diffraction patterns of BaHfSi₃O₉:Eu²⁺ with 2 mol %

and 0.5 mol % europium doping compared with undoped BaHfSi₃O₉ (measuredusing Cu Kai radiation).

FIG. 5: Emission spectra of BaHfSi₃O₉:Eu²⁺ (λ_(ex)=380 nm) with 2 mol %and 0.5 mol % europium doping.

FIG. 6: Emission spectra of BaZrSi₃O₉:Sm³⁺,Na⁺ and BaHfSi₃O₉:Sm³⁺,Na⁺(λ_(ex)=160 nm); in each case with 1 mol % doping.

FIG. 7: Emission spectra of BaZrSi₃O₉:Eu³⁺,Na⁺ and BaHfSi₃O₉:Eu³⁺,Na⁺(λ_(ex)=160 nm); in each case with 1 mol % doping.

FIG. 8: Emission spectra of BaZrSi₃O₉:Pr³⁺,Na⁺ and BaHfSi₃O₉:Pr³⁺,Na⁺(λ_(ex)=160 nm); in each case with 0.5 mol % doping.

EXAMPLES Example 1 Preparation of BaZrSi₃O₉: 0.5 mol % of Eu²⁺

1.7191 g (8.71 mmol) of BaCO₃, 1.0788 g (8.75 mmol) of ZrO₂, 1.5781 g(26.26 mmol) of SiO₂, 0.0077 g (0.022 mmol) of Eu₂O₃ and 0.1200 g (1.94mmol) of H₃BO₃ are mixed thoroughly in an agate mortar with addition ofa small amount of acetone as grinding agent. The powder is dried at 100°C. for 1 h, transferred into an aluminium oxide crucible and sintered ata temperature in the range from 1300 to 1500° C. for 2 to 4 h under acarbon monoxide atmosphere. In a second sintering step in a horizontaltubular furnace, the powder is subjected to a temperature of 1200° C.for 2 h under a stream of forming gas (10% of H₂). FIG. 2 shows theX-ray powder diffraction pattern of the compound prepared in this way.

Example 2 Preparation of BaZrSi₃O₉: 2 mol % of Eu²⁺

This compound is prepared in the same way as the compound in Example 1,with the difference that the following compounds are weighed out at thebeginning and then mixed: 1.6924 g (8.58 mmol) of BaCO₃, 1.0783 g (8.75mmol) of ZrO₂, 1.5774 g (26.25 mmol) of SiO₂, 0.0308 g (0.088 mmol) ofEu₂O₃ and 0.1200 g (1.94 mmol) of H₃BO₃. The X-ray powder diffractionpattern of this compound is likewise shown in FIG. 2.

FIG. 3 shows the emission spectra of the compounds prepared in Example 1and Example 2.

Example 3 Preparation of BaHfSi₃O₉: 0.5 mol % of Eu²⁺

This compound is prepared in the same manner as in Example 1, with thedifference that the following constituents are mixed: 1.4434 g (7.31mmol) of BaCO₃, 1.5473 g (7.35 mmol) of HfO₂, 1.3250 g (22.1 mmol) ofSiO₂, 0.0065 g (0.018 mmol) of Eu₂O₃ and 1.1200 g (1.94 mmol) of H₃BO₃.The X-ray powder diffraction pattern of this compound is shown in FIG.4.

Example 4 Preparation of BaHfSi₃O₉: 2 mol % of Eu²⁺

This compound is likewise prepared like the compound in Example 1, withthe difference that the following constituents are mixed with oneanother: 1.4211 g (7.20 mmol) of BaCO₃, 1.5467 g (7.35 mmol) of HfO₂,1.3245 g (22.0 mmol) of SiO₂, 0.0259 g (0.074 mmol) of Eu₂O₃ and 0.1200g (1.94 mmol) of H₃BO₃. The X-ray powder diffraction pattern of thiscompound is likewise shown in FIG. 4.

FIG. 5 shows the emission spectra of the compounds prepared in Examples3 and 4.

Example 5 Preparation of BaZrSi₃O₉: 1 mol % of Sm³⁺, 1 mol % of Na⁺

1.6972 g (8.60 mmol) of BaCO₃, 1.0814 g (8.78 mmol) of ZrO₂, 1.5819 g(26.33 mmol) of SiO₂, 0.0153 g (0.044 mmol) of Sm₂O₃, 0.0047 g (0.044mmol) of Na₂CO₃ and 0.1200 g (1.94 mmol) of H₃BO₃ are carefully mixedwith one another in an agate mortar with addition of a small amount ofacetone as grinding agent. The powder is dried at 100° C. for 1 h,transferred into an aluminium oxide crucible and sintered at 1300 to1500° C. for 2-4 h in air.

Example 6 Preparation of BaHfSi₃O₉: 1 mol % of Sm³⁺, 1 mol % of Na⁺

This compound is prepared in the same way as in Example 5, with thedifference that the following starting materials are mixed with oneanother: 1.4245 g (7.22 mmol) of BaCO₃, 1.5504 g (7.37 mmol) of HfO₂,1.3277 g (22.10 mmol) of SiO₂, 0.0128 g (0.037 mmol) of Sm₂O₃, 0.0039 g(0.037 mmol) of Na₂CO₃ and 0.1200 g (1.94 mmol) of H₃BO₃.

FIG. 6 shows the emission spectra of the compounds prepared in Examples5 and 6.

Example 7 Preparation of BaZrSi₃O₉: 1 mol % of Eu³⁺, 1 mol % of Na⁺

This compound is likewise prepared like the compound in Example 5, withthe difference that the following starting compounds are mixed with oneanother: 1.6971 g (8.60 mmol) of BaCO₃, 1.0814 g (8.78 mmol) of ZrO₂,1.5818 g (26.33 mmol) of SiO₂, 0.0154 g (0.044 mmol) of Eu₂O₃, 0.0047 g(0.044 mmol) of Na₂CO₃ and 0.1200 g (1.94 mmol) of H₃BO₃.

Example 8 Preparation of BaHfSi₃O₉: 1 mol % of Eu³⁺, 1 mol % of Na⁺

This compound is prepared in the same way as the compound under Example5, with the difference that the following starting compounds are mixedwith one another: 1.4244 g (7.22 mmol) of BaCO₃, 1.5504 g (7.37 mmol) ofHfO₂, 1.3277 g (22.10 mmol) of SiO₂, 0.0130 g (0.037 mmol) of Eu₂O₃,0.0039 g (0.037 mmol) of Na₂CO₃ and 0.1200 g (1.94 mmol) of H₃BO₃.

FIG. 7 shows the emission spectra of the compounds prepared in Examples7 and 8.

Example 9 Preparation of BaZrSi₃O₉: 0.5 mol % of Pr³⁺, 0.5 mol % of Na⁺

This compound is likewise prepared like the compound in Example 5, withthe difference that the following starting compounds are mixed with oneanother: 1.7128 g (8.68 mmol) of BaCO₃, 1.0803 g (8.78 mmol) of ZrO₂,1.5803 g (26.30 mmol) of SiO₂, 0.0159 g (0.022 mmol) of Pr₂(C₂O₄)₃. 10H₂O, 0.0023 g (0.022 mmol) of Na₂CO₃ and 0.1200 g (1.94 mmol) of H₃BO₃.

Example 10 Preparation of BaHfSi₃O₉: 0.5 mol % of Pr³⁺, 0.5 mol % of Na⁺

This compound is prepared in the same way as the compound in Example 5,with the difference that the following starting compounds are mixed withone another: 1.4378 g (7.29 mmol) of BaCO₃, 1.5491 g (7.36 mmol) ofHfO₂, 1.3266 g (22.08 mmol) of SiO₂, 0.0134 g (0.018 mmol) ofPr₂(C₂O₄)₃.10 H₂O, 0.0020 g (0.018 mmol) Na₂CO₃ and 1.1200 g (1.94 mmol)of H₃BO₃.

FIG. 8 shows the emission spectra of the compounds prepared in Examples9 and 10.

Example 11 Production of a pc-LED Using Compounds According to theInvention

1 g of a phosphor according to the invention from Examples 1 to 10 isdispersed with 10 g of an optically transparent silicone (OE 6550 fromDow Corning) in a Speedmixer. The silicone/phosphor mixture obtained inthis way is applied to the chip of a blue semiconductor LED (Unicornpackage from Mimaki Electronics, fitted with an InGaN chip emitting at450 nm) with the aid of an automatic dispenser (CDS 6200 from Essemtech)and cured over the course of 1 h with supply of heat in a heatingcabinet at 150° C.

Example 12 Test Results of the pc-LEDs Produced in Example 11

The LED from Example 11 is contacted with current (350 mA) using aKeithley K2400 Sourcemeter, and the optical properties are determinedusing an Instrument Systems CAS 140 spectrometer, fitted with anintegration sphere. The spectrometer software calculates the CIE 1931 xand y colour points of the LED from the emission spectrum obtained here.The corresponding values are plotted in the CIE diagram in FIG. 1.

1. Compound of the formula I(Ba_(y)Sr_(1-y))Zr_(1-x)Hf_(x)Si₃O₉   (I), where x is in the range from0 to 1 and, independently thereof, y is in the range from 0 to 1,characterised in that some of the Zr or Hf ions have been replaced byEu, Pr or Sm ions, where an alkali-metal ion is additionally present ifthe ions are trivalent.
 2. Compound according to claim 1, characterisedin that 0.1 to 20 mol %, preferably 0.2 to 10 mol %, of the Zr or Hfions have been replaced by Eu, Pr or Sm ions.
 3. Compound according toclaim 1, characterised in that the Zr or Hf ions have been replaced bydouble the amount of Eu²⁺ ions, based on the molar number of the ions.4. Compound according to claim 1, characterised in that the Zr or Hfions have been replaced by Eu³⁺ ions, Sm³⁺ ions or Pr³⁺ ions, and anamount of alkali-metal ions equivalent to the Eu³⁺ ions, Sm³⁺ ions orPr³⁺ ions is present for charge compensation.
 5. Compound according toclaim 1, characterised in that x is equal to 0 or
 1. 6. Compoundaccording to claim 1, characterised in that 0≦y<0.3, preferably y=0, orin that 0.7<y≦1, preferably y=1.
 7. Process for the preparation of acompound according to claim 1, comprising the following process steps:a) provision of a barium and/or strontium source, a zirconium or hafniumsource, a silicon source and a source of one of the metals samarium,praseodymium or europium; b) mixing of the sources provided in step a);and c) temperature treatment of the sources mixed in step b) in therange from 1000 to 1700° C.
 8. A conversion phosphor which comprises acompound according to claim
 1. 9. Emission-converting materialcomprising a compound according to claim
 1. 10. Emission-convertingmaterial according to claim 9, which additionally comprises at least onefurther conversion phosphor, where the further conversion phosphor ispreferably selected from the group consisting of sulfides, silicates,aluminates, borates, nitrides, oxynitrides, siliconitrides andalumosiliconitrides which are doped with Eu²⁺, Ce³⁺ or Mn²⁺.
 11. Lightsource, characterised in that it contains a primary light source and anemission-converting material according to claim
 9. 12. Light sourceaccording to claim 11, characterised in that the primary light source isa luminescent indium aluminium gallium nitride.
 13. Lighting unit, inparticular for the backlighting of display devices, characterised inthat it contains at least one light source according to claim
 11. 14.Display device, in particular liquid-crystal display device (LCdisplay), characterised in that it contains at least one lighting unitaccording to claim 13.